CN111289085B - Microphone diaphragm amplitude measuring method and device - Google Patents
Microphone diaphragm amplitude measuring method and device Download PDFInfo
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- CN111289085B CN111289085B CN202010087204.9A CN202010087204A CN111289085B CN 111289085 B CN111289085 B CN 111289085B CN 202010087204 A CN202010087204 A CN 202010087204A CN 111289085 B CN111289085 B CN 111289085B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
- G01H9/006—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors the vibrations causing a variation in the relative position of the end of a fibre and another element
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R29/00—Monitoring arrangements; Testing arrangements
- H04R29/004—Monitoring arrangements; Testing arrangements for microphones
Abstract
A method and device for measuring the vibration amplitude of microphone diaphragm includes single-mode optical fibre, microphone to be measured, sound source, light source, spectrum detection module and control and signal processing unit. The device utilizes a single mode fiber and a local area of a tested microphone diaphragm to form a Fabry-Perot (FP) interference cavity; making incident light enter the FP interference cavity through the single mode fiber to generate interference light; controlling a sound source to emit sound waves to excite the vibration diaphragm to vibrate, and continuously detecting interference light generated by the FP interference cavity when the vibration diaphragm vibrates by using a spectrum detection module to obtain a plurality of interference spectrums; and processing the plurality of interference spectrums to obtain a plurality of cavity lengths of the FP interference cavity when the diaphragm vibrates, and determining the amplitude of the local area of the diaphragm according to the cavity lengths. The device has simple structure, convenient use and high measurement precision, is suitable for measuring the mechanical sensitivity of various microphones, can measure the vibration amplitude of the vibrating diaphragm on line in the manufacturing process of the microphone, can optimize the manufacturing process and improve the consistency of devices.
Description
Technical Field
The invention relates to the technical field of optical measurement, in particular to a microphone diaphragm amplitude measurement method and device.
Background
The accurate measurement of the amplitude of the microphone diaphragm is crucial to the design, preparation, process optimization, performance evaluation and the like of the microphone, and requires that the used instrument and method have dynamic micro-displacement measurement capability, and the vibration of the diaphragm cannot be disturbed in the test process so as to ensure the accuracy of the test result. The traditional microphone diaphragm amplitude measurement method is generally an electrical measurement method, and the method requires that the microphone diaphragm to be measured is simultaneously used as one of the measurement electrodes, so that the method is only suitable for measuring the metal diaphragm, and the electrostatic action existing between the electrodes can cause interference on the vibration of the metal diaphragm, thereby influencing the measurement result. Compared with the traditional dynamic micrometric displacement electrical measurement method, the technology for optically measuring the dynamic micrometric displacement allows non-contact measurement, the vibration of the vibrating diaphragm cannot be interfered in the measurement process, the anti-electromagnetic interference effect is realized, the sensitivity is high, the accuracy and the reliability are realized, the spatial resolution is high, the amplitude of the local area of the vibrating diaphragm can be measured, the response speed is high, and the dynamic range is wide.
Common optical micro-displacement measurement systems include laser triangulation, fiber grating, laser interferometry, and the like. For example, a laser micro-displacement measurement system based on the doppler effect can accurately measure the amplitude of the microphone diaphragm micro-displacement, but the equipment has the disadvantages of high manufacturing cost, complex structure, complex operation, narrow measurement dynamic range and high use cost. In order to overcome the above problems, it is necessary to develop an optical measurement method that has a simple structure, is convenient to operate, has low measurement cost, and is suitable for accurately measuring the amplitudes of various microphone diaphragms.
Disclosure of Invention
In view of the above, the present invention provides a method and an apparatus for measuring an amplitude of a microphone diaphragm, so as to at least partially solve at least one of the above-mentioned technical problems.
To achieve the above object, as one aspect of the present invention, there is provided a microphone diaphragm amplitude measuring apparatus, comprising: single mode fiber, surveyed microphone, sound source, light source, spectrum detection module and control and signal processing unit, wherein: the single-mode optical fiber comprises a first end face and a second end face which are positioned at two ends, and the first end face is a plane vertical to the optical fiber axis; the tested microphone is provided with a vibrating diaphragm with a reflective surface, and a local area of the vibrating diaphragm is right opposite to the first end face of the single-mode optical fiber to form a Fabry-Perot interference cavity; the sound source is used for generating single-frequency sound waves to excite the diaphragm of the microphone to be tested to vibrate; the light source is used for providing incident light which can be incident to the Fabry-Perot interference cavity through the single-mode optical fiber and generate interference light through the Fabry-Perot interference cavity; the spectrum detection module is used for continuously detecting interference light generated by the Fabry-Perot interference cavity when a vibrating diaphragm of the microphone to be detected vibrates at a preset spectrum sampling rate to obtain a plurality of interference spectrums; and the control and signal processing unit is used for controlling the sound wave frequency and the sound pressure generated by the sound source and processing a plurality of interference spectrums output by the spectrum detection module so as to obtain a plurality of cavity lengths of the Fabry-Perot interference cavity during the vibration period of the vibrating diaphragm, and determining the amplitude of the local area of the vibrating diaphragm according to the change of the cavity lengths along with time.
As another aspect of the present invention, there is also provided a method for measuring an amplitude of a microphone diaphragm using the microphone diaphragm amplitude measuring apparatus as described above, including the steps of: step A: the first end face of the single-mode optical fiber is right opposite to a local area of a diaphragm of a microphone to be detected so as to form a Fabry-Perot interference cavity; and B: starting a light source and a spectrum detection module, and enabling incident light provided by the light source to be incident to the Fabry-Perot interference cavity through the single-mode optical fiber to generate interference light; and C: controlling the sound source to emit at a frequency f0The spectrum detection module is utilized to continuously detect interference light generated by the Fabry-Perot interference cavity during the vibration period of the diaphragm of the microphone to be detected at a preset spectrum sampling rate, so as to obtain a plurality of interference spectrums; step D: and processing the plurality of interference spectrums output by the spectrum detection module by using a control and signal processing unit to obtain a plurality of cavity lengths of the Fabry-Perot interference cavity during the vibration period of the diaphragm, and determining the amplitude of the local area of the diaphragm according to the change of the cavity lengths along with time.
Compared with the prior art, the microphone diaphragm amplitude measuring method and the microphone diaphragm amplitude measuring device have at least one or part of the following beneficial effects:
(1) the invention adopts the optical fiber Fabry-Perot interference spectrum measurement method, changes the cavity length of the optical fiber Fabry-Perot interference cavity based on the vibration displacement change of the local area of the microphone vibrating diaphragm, and realizes the amplitude measurement of the local area of the vibrating diaphragm by measuring the dynamic cavity length of the optical fiber Fabry-Perot interference cavity, and the method has good three-dimensional spatial resolution;
(2) the microphone diaphragm amplitude measuring method and the device thereof have no limitation on the structure and the material of the microphone diaphragm, can measure the amplitude of a common circular metal diaphragm of the microphone, can also measure the amplitude of a circular nonmetal such as a glass diaphragm, can also measure the amplitude of a noncircular MEMS diaphragm such as a cantilever beam type, an I-shaped type and the like, and have wide application range;
(3) according to the invention, a first end face of the single-mode optical fiber, which is perpendicular to an optical fiber axis, and a vibrating diaphragm of a microphone to be detected form a Fabry-Perot interference cavity, light transmitted by the single-mode optical fiber is transmitted in the same path, and the single-mode optical fiber does not introduce optical path difference change, so that the generated interference light is only modulated by cavity length change, and the interference spectrum accurately reflects the distance change of the vibrating diaphragm, and has high precision and sensitivity;
(4) the optical measurement device has the advantages that each measurement component of the required optical measurement device is independently arranged outside the microphone to be measured, the structure is simple, the volume is small, the cost is low, the realization is easy, and the popularization and application values in the aspects of microphone manufacturing process control, performance test and the like are high.
Drawings
Fig. 1 is a schematic structural diagram of a microphone diaphragm amplitude measuring device in embodiment 1 of the present invention;
fig. 2 is a fabry-perot interference spectrum obtained by using the microphone diaphragm amplitude measurement apparatus according to embodiment 1 of the present invention, in a case where a circular glass diaphragm of a microphone to be measured is not excited by sound waves;
fig. 3 is a flowchart of a method for measuring the amplitude of a microphone diaphragm according to embodiment 1 of the present invention;
fig. 4A is a schematic diagram of selecting two adjacent wave troughs from an obtained fabry-perot interference spectrum to obtain a cavity length of a fabry-perot interference cavity according to embodiment 1 of the present invention;
fig. 4B is a schematic diagram of obtaining a cavity length of a fabry-perot interference cavity by selecting adjacent peaks and troughs in an obtained fabry-perot interference spectrum according to embodiment 1 of the present invention;
fig. 5A is a data point and a fitting curve of the data point of the cavity length of the fabry-perot interference cavity corresponding to the central region of the circular glass diaphragm of the microphone to be tested, which is excited by sound waves with a frequency of 1000Hz and a sound pressure of 4pa according to embodiment 1 of the present invention, along with time;
fig. 5B is a data point and a fitting curve thereof of the amplitude of the central region of the circular glass diaphragm of the microphone to be tested, which changes with the sound pressure under the excitation of sound waves with a frequency of 1000Hz in accordance with embodiment 1 of the present invention;
fig. 6A is a data point and a fitting curve of the data point of the cavity length of the fabry-perot interference cavity corresponding to the central region of the circular metal diaphragm of the microphone to be tested, which is excited by sound waves with a frequency of 500Hz and a sound pressure of 5pa according to embodiment 2 of the present invention, along with time;
fig. 6B is a data point and a fitting curve thereof of the amplitude of the central area of the circular metal diaphragm of the microphone to be tested, which changes with the sound pressure under the excitation of sound waves with a frequency of 500Hz in accordance with embodiment 2 of the present invention;
fig. 6C is a data point and a fitting curve thereof of the amplitude of the central area of the circular metal diaphragm of the microphone to be tested, which changes with the acoustic wave frequency under the excitation of the acoustic wave with the acoustic pressure of 1Pa according to embodiment 2 of the present invention;
fig. 7A is a data point of the cavity length of the fabry-perot interference cavity corresponding to the farthest end region of the H-type MEMS silicon diaphragm changing with time and a fitting curve thereof (an inset is a real photograph of the H-type MEMS silicon diaphragm) under the excitation of sound waves with a frequency of 322Hz and a sound pressure of 270mpa by the H-type MEMS silicon diaphragm of the microphone to be tested of the invention 3;
fig. 7B is a data point of a change of a cavity length of the fabry-perot interference cavity corresponding to the farthest end region of the H-type MEMS silicon diaphragm with time under the excitation of the acoustic wave with the frequency of 622Hz and the acoustic pressure of 98mPa, and a fitting curve thereof in the microphone according to embodiment 3 of the present invention.
In the above drawings, the reference numerals have the following meanings:
10-a light source; 20-single mode fiber; 30-a fiber optic circulator;
40-a sound source; 50-a microphone to be tested; 60-standard sound level meter;
70-a spectral detection module; 80-a control and signal processing unit; 90-precision moving platform;
91-microphone fixture; 92-single mode fiber securing member; 93-monocular video microscope;
100-case.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to specific embodiments and the accompanying drawings. It should be noted that in the drawings or description, the same drawing reference numerals are used for similar or identical parts. Implementations not depicted or described in the drawings are of a form known to those of ordinary skill in the art. Additionally, while exemplifications of parameters including particular values may be provided herein, it is to be understood that the parameters need not be exactly equal to the respective values, but may be approximated to the respective values within acceptable error margins or design constraints. Directional phrases used in the embodiments, such as "upper," "lower," "front," "rear," "left," "right," and the like, refer only to the orientation of the figure. Accordingly, the directional terminology used is intended to be in the nature of words of description rather than of limitation.
The invention discloses a method and a device for measuring the amplitude of a microphone diaphragm, which are used for measuring the distance change between a flat-end optical fiber end face and the microphone diaphragm by using the principle of optical fiber Fabry-Perot (FP) interference spectrum, thereby reflecting the amplitude change of a local area of the microphone diaphragm and realizing the measurement of the micro-displacement of the local area of the microphone diaphragm. The required whole measuring system has simple structure and low cost, is beneficial to operation and easy to realize, and is generally suitable for various laboratory environments.
The following describes a method and an apparatus for measuring the amplitude of a diaphragm of a microphone according to the present invention with reference to specific embodiments. It should be noted that the following specific examples are only for illustration and are not intended to limit the invention.
Example 1
In a first exemplary embodiment of the present invention, a microphone diaphragm amplitude measurement apparatus is provided. Fig. 1 is a schematic structural diagram of a microphone diaphragm amplitude measuring device according to the present invention. As shown in fig. 1, the microphone diaphragm amplitude measuring apparatus includes: single mode fiber 20, microphone 50 under test, sound source 40, light source 10, spectrum detection module 70 and control and signal processing unit 80, wherein: the single-mode optical fiber 20 includes a first end face and a second end face at both ends, the first end face being a plane perpendicular to the optical fiber axis; the microphone 50 to be tested has a vibrating diaphragm with a reflective surface, and a local area of the vibrating diaphragm is right opposite to the first end face of the single-mode optical fiber to form a Fabry-Perot interference cavity; the sound source 40 is used for generating single-frequency sound waves to excite the diaphragm of the microphone to be tested to vibrate; the light source 10 is configured to provide incident light, which can be incident into the fabry-perot interference cavity through the single-mode fiber 20 and generate interference light through the fabry-perot interference cavity; the spectrum detection module 70 is configured to continuously detect interference light generated by the fabry-perot interference cavity when the diaphragm of the microphone 50 to be detected vibrates at a preset spectrum sampling rate, so as to obtain a plurality of interference spectra; the control and signal processing unit 80 is configured to control the sound wave frequency and the sound pressure generated by the sound source 40, and process the multiple interference spectra output by the spectrum detection module 70, so as to obtain multiple cavity lengths of the fabry-perot interference cavity when the diaphragm vibrates, and determine the amplitude of the local region of the diaphragm according to the change of the multiple cavity lengths with time.
The design principle of the microphone diaphragm amplitude measuring device provided by the invention is as follows: the method comprises the steps that a microphone vibrating diaphragm is excited by an acoustic signal to vibrate to enable the vibrating diaphragm to generate dynamic micro-displacement, the dynamic micro-displacement of a local area of the vibrating diaphragm is converted into the change of optical fiber Fabry-Perot interference light phase difference (namely the cavity length change of an optical fiber Fabry-Perot interference cavity) by utilizing an optical fiber Fabry-Perot interference technology, the cavity lengths at different moments are obtained through interference spectrum measurement with high time resolution, further, a time-cavity length dependency relation curve is established, and optimal fitting is carried out on the curve based on a vibration equation, so that the amplitude of the local area of the vibrating diaphragm can be accurately obtained.
The following describes each component of the microphone diaphragm amplitude measuring device of the present embodiment in detail.
In the present embodiment, the light source 10 may be an ASE light source, an LED light source or a halogen tungsten lamp, without any particular limitation, and according to the conventional knowledge in the art for the light source 10, the spectral bandwidth thereof generally does not exceed 600 nm, and in the present embodiment, the spectral bandwidth thereof preferably does not exceed 50 nm, and preferably is greater than 20 nm, and if the spectral bandwidth is too small, it is difficult to ensure that at least one peak and at least one valley can appear in the interference spectrum; and the spectral bandwidth is too wide, so that the spectral detection module is longer in time use when recording the spectrum, the time resolution of spectral detection is sacrificed, and the accurate measurement of the amplitude of the microphone diaphragm under the excitation of higher audio frequency is not facilitated.
In this embodiment, the operating wavelength of the light source 10 is 1527.2280nm to 1567.9560nm, and the spectrum detection module is matched with the operating wavelength of the light source, but the light source, the spectrum detection module and the control and signal processing unit may be integrated in different embodiments, but not limited thereto.
In this embodiment, the single-mode fiber 20 is a quartz fiber, and the first end face thereof is a plane perpendicular to the fiber axis as an exit end face, so that the first end face and the diaphragm of the microphone 50 to be measured form two parallel reflection surfaces, thereby forming a fabry-perot interference cavity; in addition, a multimode fiber cannot be adopted, but only the single-mode fiber 20 can be used for transmitting incident light, because the single-mode fiber 20 only allows single-guide-mode transmission, the multimode interference phenomenon cannot occur, the optical path difference cannot be introduced, and the generated interference light is only modulated by the cavity length change, so that the distance change of the diaphragm can be accurately reflected by the subsequently obtained interference spectrum, and the interference of light among different modes can be caused when the incident light is transmitted in the multimode fiber in multiple modes, and the obtained interference spectrum is difficult to accurately reflect the distance change of the diaphragm, which is not beneficial to the accurate measurement of the amplitude of the diaphragm of the microphone to be measured.
In the present embodiment, the distance between the first end face of the single-mode fiber 20 and the local region of the diaphragm is configured to make the interference spectrum have at least one peak and at least one valley, where "making the interference spectrum have at least one peak and at least one valley" means that the light intensity can reach at least one peak and at least one valley as the wavelength changes in an interference spectrum, and specifically, in different embodiments, the light intensity can only include one peak and one valley, or only include two peaks and one valley, or only include one peak and two valleys, or include more than two peaks and more than two valleys, and the interference spectrum can have 9 peaks and 8 valleys with reference to the spectrum obtained by the measured microphone without the sound source as shown in fig. 2.
In this embodiment, the microphone diaphragm amplitude measurement device further comprises a fiber optic circulator 30 comprising a first port 1, a second port 2 and a third port 3, wherein: the first port 1 is an input end and is connected with a light source 10 through an optical fiber; the second port 2 is an output port and is connected with the spectrum detection module 70 through an optical fiber; and a third port 3, which is butted against a second end face of the single mode optical fiber 20. In other embodiments, the fiber circulator 30 may be replaced with a one-to-two fiber splitter or the like.
In the present embodiment, the microphone 50 to be measured is one of an electret microphone, a MEMS microphone, a fiber-optic microphone, and a grating microphone; in other embodiments, the microphone 50 to be measured may also be a component of an electret microphone, a MEMS microphone, a fiber optic microphone, or a grating microphone that includes a diaphragm. It should be appreciated that to facilitate measurement, the microphone 50 under test has to have its diaphragm exposed to air before testing. The surface of the diaphragm of the tested microphone 50 is reflective and is an elastic diaphragm, and when an acoustic signal acts on the tested microphone, the elastic diaphragm deforms, so that the optical signal reflected back to the optical fiber is subjected to acoustic wave modulation. Specifically, the diaphragm may be a diaphragm formed by one of metal, glass, graphene, silicon, polymer, metal oxide, and silicon nitride, or a composite diaphragm formed by a plurality of the above diaphragm materials.
The diaphragm may have any shape and size, and is not particularly limited, and in this embodiment, a circular glass diaphragm is taken as an example, the thickness of the glass diaphragm is 50 micrometers, the periphery of the diaphragm is fixed, and the diameter of the inner circle of the diaphragm is 0.5 inches. Since the single-mode fiber 20 (the core diameter of which is generally not more than 10 μm) is much smaller than the size of a conventional diaphragm, the "local area" of the diaphragm directly opposite to the single-mode fiber 20 corresponds to a vibration point on the diaphragm, and by adjusting different positions of the first end surface of the single-mode fiber 20 relative to the diaphragm, the amplitude distribution of the diaphragm along a certain direction can be measured.
In this embodiment, the central region of the diaphragm is taken as an example, and the central region has the maximum amplitude for a diaphragm with a fixed periphery, and the first end face of the single-mode fiber 20 and the central region of the diaphragm opposite to the first end face form a fabry-perot interference cavity, but the invention is not limited thereto.
In this embodiment, the microphone diaphragm amplitude measuring device further includes a standard sound level meter 60, configured to measure sound pressure of the sound wave generated by the sound source 40 reaching the microphone diaphragm to be measured, and in practical application, the performance of the microphone diaphragm to be measured may be evaluated by combining the sound pressure of the sound wave and the obtained diaphragm amplitude; in other embodiments, the standard sound level meter 60 may also be replaced with a standard microphone.
In this embodiment, the preset spectrum sampling rate of the spectrum detection module 70 is preferably greater than 2 times of the frequency of the sound wave generated by the sound source, and it can be understood that one detected interference spectrum represents the modulation spectrum of the fabry-perot interference cavity corresponding to the displacement of the local region of the diaphragm at a certain time to the incident light, so that, as the spectrum sampling rate increases, it is beneficial to obtain a plurality of interference spectra corresponding to different diaphragm displacements in the vibration period of the diaphragm excited by the sound wave, and it is more beneficial to accurately determine the amplitude of the local region of the diaphragm through fitting in the following process. For the same reasons as described above, the present embodiment preferably obtains not less than 3 interference spectra from the spectrum detection module during each test to ensure that the amplitude of the local region of the diaphragm can be accurately determined by fitting.
It is understood that the detection spectral range of the spectral detection module 70 should include the output spectral range of the light source 10, which has a fast response capability and a fast spectral output capability to the light source light. The light detection component of the spectrum detection module 70 includes a CCD or CMOS array photosensitive chip, and is commercially available, and the structure thereof is not described herein.
In this embodiment, the control and signal processing unit 80 may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. Its various component embodiments may be implemented in hardware, or in conventional software modules running on one or more processors, or in a combination of both. It will be appreciated by those skilled in the art that existing programming language or code may be used for a particular programming language, but that the present invention is not concerned with procedural modifications.
In this embodiment, the microphone diaphragm amplitude measuring apparatus further includes a precision moving platform 90, configured to fix the measured microphone 50 and the single-mode fiber 20, and adjust a position of the single-mode fiber relative to the measured microphone, so that the first end surface of the single-mode fiber 20 and a local region of the diaphragm of the measured microphone 50 form the fabry-perot interference cavity. More specifically, the precision moving platform 90 is provided with a microphone fixing member 91 and a single-mode fiber fixing member 92, and the precision moving platform 90 enables the microphone fixing member 91 and/or the single-mode fiber fixing member 92 to translate, lift or rotate under manual or automatic operation, and the adjustment precision can preferably reach the micrometer level, so as to ensure that the first end face of the single-mode fiber 20 and a local area of the diaphragm of the microphone 50 to be measured can easily form the fabry-perot interference cavity.
In this embodiment, the microphone diaphragm amplitude measuring apparatus further includes at least one monocular video microscope 93 fixed on the precision moving platform 90 for monitoring the relative position between the first end surface of the single-mode optical fiber 20 and the local region of the diaphragm of the microphone 50 to be measured. Compared with the naked eye, the monocular video microscope 93 can more accurately monitor the relative position between the first end face of the single-mode optical fiber and the local area of the diaphragm of the microphone to be detected; the monocular video microscope can be obtained by adopting a conventional structure in the field and is commercially available, and the structure of the monocular video microscope is not described herein.
In this embodiment, the microphone diaphragm amplitude measuring device further includes a case 100, in which the single mode fiber 20, the sound source 40, the microphone 50 to be measured, the standard sound level meter 60, the precision moving platform 90, and the components (including the microphone fixing member 91, the single mode fiber fixing member 92, the single-tube video microscope 93, etc.) mounted on the precision moving platform 90 are disposed. The case 100 is used for isolating the vibration of the device support body in the measurement process, isolating the ambient noise around the device, eliminating the echo of the single-frequency sound wave emitted by the loudspeaker and creating conditions for improving the measurement precision. In the present embodiment, the light source 10, the fiber optic circulator 30, the spectrum detection module 70, and the control and signal processing unit 80 are disposed outside the casing 100. It is noted that some or all of these components may be disposed inside the chassis 100 as desired. In addition, the cabinet 100 needs to be designed and manufactured to meet the requirements of echo cancellation, vibration isolation and noise isolation.
The embodiment of the invention has the following effects: the method realizes measurement of the amplitude of the microphone diaphragm in a local area, and characterizes and determines the mechanical sensitivity and frequency response characteristics of the microphone. So far, the description of the microphone diaphragm amplitude measuring device according to the first embodiment of the present invention is completed.
In a first exemplary embodiment of the present invention, a method for measuring the amplitude of a diaphragm of a microphone is also provided; fig. 2 is a fabry-perot interference spectrum obtained by using the microphone diaphragm amplitude measurement apparatus according to embodiment 1 of the present invention, in a case where the circular glass diaphragm of the microphone to be measured is not excited by sound waves. Fig. 3 is a flowchart of a method for measuring the amplitude of a microphone diaphragm according to embodiment 1 of the present invention; fig. 4A is a schematic diagram of selecting two adjacent wave troughs from an obtained fabry-perot interference spectrum to obtain a cavity length of a fabry-perot interference cavity according to embodiment 1 of the present invention; fig. 4B is a schematic diagram of obtaining a cavity length of a fabry-perot interference cavity by selecting adjacent peaks and troughs in an obtained fabry-perot interference spectrum according to embodiment 1 of the present invention;
the method for measuring the amplitude of the microphone diaphragm in this embodiment is based on the device for measuring the amplitude of the microphone diaphragm in embodiment 1, and it can be understood that the construction of the device for measuring in embodiment 1 should be completed first, including the operations of supplying power to the light source, the spectrum detection module and the monocular video microscope, fixing the microphone to be measured on the precision mobile platform, and the like. On this basis, as shown in fig. 3, the measurement method specifically includes the following steps:
step A: and the first end face of the single-mode optical fiber is right opposite to the local area of the diaphragm of the microphone to be detected so as to form a Fabry-Perot interference cavity.
The microphone to be tested of the embodiment is provided with a circular glass vibrating diaphragm, the thickness of the glass vibrating diaphragm is 50 micrometers, the periphery of the vibrating diaphragm is fixed, and the diameter of the inner circle of the vibrating diaphragm is 0.5 inch. At this time, the central region of the circular glass diaphragm has the maximum amplitude, and as an example, in the present embodiment, the first end face of the single-mode optical fiber is directed toward the central region of the diaphragm of the microphone to be measured to constitute a fabry-perot interference cavity. It will be appreciated that by adjusting a plurality of other positions of the first end face of the single mode optical fibre 20 relative to the diaphragm, a one-dimensional or (and) two-dimensional distribution of the amplitude of the diaphragm can be measured.
And B: and starting the light source and the spectrum detection module to enable incident light provided by the light source to be incident to the Fabry-Perot interference cavity through the single-mode optical fiber to generate interference light.
Optionally, after the step B, the method further includes a step B': and enabling the first end face of the single-mode optical fiber to gradually approach to a local area of a diaphragm of the microphone to be detected along a direction perpendicular to the first end face until the interference spectrum obtained by the spectrum detection module can generate at least 1 peak and at least 1 trough, and then stopping approaching. In the step, the single-mode fiber is slid to gradually approach the local area of the diaphragm, the spectrum detection module is used for measuring the interference spectrum in real time, and when 9 peak values of the interference spectrum are observed, the movement of the first end face of the single-mode fiber is stopped.
Preferably, the position of the first end face of the single-mode optical fiber relative to a local region of the diaphragm is monitored using a monocular video microscope, so that the relative position can be accurately adjusted.
And C: controlling the sound source to emit at a frequency f0The spectrum detection module is used for continuously detecting interference light generated by the Fabry-Perot interference cavity when the vibrating diaphragm of the microphone to be detected vibrates at a preset spectrum sampling rate to obtain a plurality of interference spectrums;
in this step, f0For example, 1kHz can be taken as an example, but not limited thereto; correspondingly, the spectrum detection module continuously records not less than 3 interference spectrums at a spectrum sampling rate of more than 2kHz, and each interference spectrum corresponds to a specific moment.
Step D: and processing the plurality of interference spectra output by the spectrum detection module by using the control and signal processing unit to obtain a plurality of cavity lengths of the Fabry-Perot interference cavity when the vibrating diaphragm vibrates, and determining the amplitude of the local area of the vibrating diaphragm according to the change of the cavity lengths along with time.
The method comprises the following steps of calculating the cavity length of an interference cavity based on the interference principle of a Fabry-Perot interference cavity and the wavelength of a wave crest or a wave trough of an interference spectrum, and calculating the amplitude of a local area of a vibrating diaphragm according to the cavity length fitting; however, because the formula satisfied by the wavelengths corresponding to the peaks and the troughs is different (as shown in the following formula), the calculation for obtaining the specific cavity length can adopt the following two ways, which are slightly different from each other:
the wave length corresponding to the wave trough satisfies the formula
The wavelength corresponding to the wave crest satisfies the formula:
specifically, as shown in fig. 4A, taking the selection of two adjacent troughs as an example, step D specifically includes:
substep D1: processing each interference spectrum by using smooth denoising and interpolation fitting algorithms respectively, and processing each interference spectrum at time t1～tnObtaining, wherein n is the number of interference spectra;
substep D2: respectively determining the wavelength lambda of two adjacent wave troughs in each processed interference spectrum1、λ2Formula (ii)
It is deduced based on the formula satisfied by the wavelength corresponding to the wave trough, wherein L is the cavity length of the Fabry-Perot interference cavity, and the cavity length L corresponding to each interference spectrum can be calculated1～Ln(ii) a It can be understood that if two adjacent peaks are selected, the formula can be derived based on the formula satisfied by the wavelengths corresponding to the peaks
Substep D3: an array (t) is formed by the cavity lengths and the moments corresponding to the respective interference spectra1、L1)、(t2、L2)…(tn、Ln) Substituting into the equation of vibration
Calculating the amplitude DeltaL of the local area of the tested microphone diaphragm, wherein L0Is the cavity length, f, of the diaphragm in the rest state0Is the acoustic frequency, t is the time of day,
is the phase difference between the vibration of the diaphragm and the sound wave.
As shown in fig. 4B, taking a pair of adjacent troughs and peaks as an example, step D specifically includes:
sub-step D1': processing each interference spectrum by using smooth denoising and interpolation fitting algorithms respectively, and processing each interference spectrum at time t1～tnObtaining, wherein n is the number of interference spectra;
sub-step D2': respectively determining the wavelength lambda of a pair of adjacent peaks and troughs in each interference spectrum after processing1、λ2Based on the formula
It is deduced based on the formula satisfied by the wavelengths respectively corresponding to the wave crests and the wave troughs, wherein L is the cavity length of the Fabry-Perot interference cavity, and the cavity length L corresponding to each interference spectrum is obtained by calculation1～Ln；
Sub-step D3': an array (t) is formed by the cavity lengths and the moments corresponding to the respective interference spectra1、L1)、(t2、L2)…(tn、Ln) Substituting into the equation of vibration
Calculating the amplitude DeltaL of the local area of the tested microphone diaphragm, wherein L0Is the cavity length, f, of the diaphragm in the rest state0Is the acoustic frequency, t is the time of day,
is the phase difference between the vibration of the diaphragm and the sound wave.
In the sub-step D3 or D3', the calculation of the amplitude Δ L of the local region of the measured microphone diaphragm by substituting the vibration equation is performed by data fitting, and the fitting result is shown in fig. 5A. Fig. 5A is a data point of a cavity length of a fabry-perot interference cavity corresponding to a central region of a circular glass diaphragm of a microphone to be tested, which is excited by sound waves with a frequency of 1000Hz and a sound pressure of 4pa, changing with time and a fitting curve thereof according to embodiment 1 of the present invention. It can be seen from the figure that the cavity length is periodically vibrated with time, the vibration frequency is 1000Hz, and the frequency is the same as that of the excitation sound wave. Half of the difference between the cavity lengths corresponding to the adjacent peaks and valleys is the amplitude of the central region of the circular glass diaphragm of the tested microphone, and the amplitude is 400 nanometers. Fig. 5B is a data point and a fitting curve thereof of the amplitude of the central region of the circular glass diaphragm of the microphone to be tested, which changes with the sound pressure under the excitation of sound waves with the frequency of 1000Hz in accordance with the present invention. As can be seen from the figure, the amplitude of the central region of the diaphragm is linear with the sound pressure. The test result indicates that the microphone diaphragm amplitude measuring method and the device thereof are suitable for measuring the mechanical sensitivity of the microphone.
Thus, the method for measuring the amplitude of the diaphragm of the microphone according to the first embodiment of the present invention has been described.
Example 2
To further illustrate the effective application of the microphone diaphragm amplitude measuring device of the present invention, in this embodiment, a microphone including a circular metal diaphragm with a diameter of 0.5 inch and a thickness of 3 μm is selected as a microphone to be measured, and the amplitude of the central area of the diaphragm of the microphone to be measured is measured by using the measuring device and the measuring method of embodiment 1. The acoustic frequency was set to 500Hz during the measurement, and the measurement procedure was the same as in steps A to D of example 1.
Fig. 6A shows data points of the cavity length of the fabry-perot interference cavity corresponding to the central region of the circular metal diaphragm of the microphone under the excitation of the sound wave with the frequency of 500Hz and the sound pressure of 5pa, and the fitting curve thereof according to the embodiment 2 of the present invention. It can be seen from the figure that the cavity length is periodically vibrated with time, the vibration frequency is 500Hz, and the frequency is the same as that of the excitation sound wave. Half of the difference between the cavity lengths corresponding to the adjacent peaks and valleys is the amplitude of the central region of the circular metal diaphragm of the tested microphone, and the amplitude is 62.5 nanometers. Fig. 6B is a data point of the amplitude of the central area of the circular metal diaphragm of the microphone to be tested, which changes with the sound pressure under the excitation of the sound wave with the frequency of 500Hz, and a fitting curve thereof in embodiment 2 of the present invention. It can be seen from the figure that the amplitude of the central region of the diaphragm is in a linear relationship with the sound pressure, which also shows that the variation relationship between the amplitude and the sound pressure of the diaphragm of the microphone can be obtained by the measuring method of the present invention, that is, the measuring method of the present invention can obtain the mechanical sensitivity of the microphone. Fig. 6C shows data points of the amplitude of the central region of the circular metal diaphragm of the microphone to be tested, which changes with the acoustic frequency under the excitation of the acoustic wave with the acoustic pressure of 1Pa, and a fitting curve thereof in accordance with embodiment 2 of the present invention. It can be seen from the figure that the amplitude of the central region of the circular metal diaphragm is almost constant at a given acoustic pressure when the acoustic frequency varies within the range of 100Hz to 1000 Hz. The results show that the measuring method and the device thereof can be used for acquiring the frequency response curve of the microphone.
In this embodiment, it should be noted that the circular metal diaphragm of the microphone to be tested is flexible before being fixed to the diaphragm support, and has no elastic vibration capability. In order to make the circular metal diaphragm have elastic vibration capability after being fixed with the diaphragm support, the metal diaphragm needs to be prestressed, and the amplitude of the diaphragm depends on the magnitude of the prestress applied to the diaphragm. The vibrating diaphragm is vibrated by sound wave excitation in the process of applying prestress to the vibrating diaphragm, the amplitude change of the central area of the vibrating diaphragm is measured on line by using the device for measuring the amplitude of the vibrating diaphragm of the microphone, when the amplitude reaches a preset value, the prestress is stopped to be continuously applied, and then the vibrating diaphragm is firmly welded with the support, so that the prepared microphone is ensured to have good consistency. As mentioned above, the microphone diaphragm amplitude measuring method and the device thereof can be used for controlling and optimizing the microphone preparation process.
Thus, the method for measuring the amplitude of the diaphragm of the microphone according to the second embodiment of the present invention has been described.
Example 3
The microphone diaphragm amplitude measuring device is not only suitable for measuring the amplitude of the local area of the circular diaphragm, but also can measure the amplitude of the diaphragm with a non-circular structure. The most common diaphragms of non-circular configuration include MEMS cantilever diaphragms and H-shaped (also known as i-shaped) MEMS diaphragms. In order to verify the effect of the amplitude measuring device of the microphone diaphragm of the present invention on the amplitude of the non-circular diaphragm local region, the present example prepares an H-shaped silicon diaphragm on an SOI substrate by using an MEMS process (see the inset in fig. 7A). The H-type MEMS silicon diaphragm is provided with two square wings with the side length of 3mm, the adjacent edges of the two wings are connected by a silicon bridge with the length of 1mm, the upper side and the lower side of the middle of the silicon bridge are respectively provided with an anchor point, and the whole H-type MEMS silicon diaphragm is in coplanar connection with an SOI substrate through the two anchor points. The H-shaped MEMS silicon diaphragm has two vibration modes, one is a swinging mode with the resonant frequency of 322Hz, and the other is a bending mode with the resonant frequency of 622 Hz. In this embodiment, the amplitude of the farthest end of the H-type MEMS silicon diaphragm at the two resonant frequencies is measured by using the microphone diaphragm amplitude measuring apparatus of the present invention. Before the test starts, firstly, an H-shaped MEMS silicon vibrating diaphragm is fixed on a specially-made support, then the support with the H-shaped MEMS silicon vibrating diaphragm is fixed by a microphone fixing piece on a precise moving platform, the position of a single-mode optical fiber is adjusted, the first end face of the single-mode optical fiber is aligned to the farthest end of the H-shaped MEMS silicon vibrating diaphragm, so that a Fabry-Perot interference cavity is formed, then the measurement is carried out according to the same steps as the embodiment 1, and the amplitude of the farthest end of the H-shaped MEMS silicon vibrating diaphragm under the given sound pressure and the given audio frequency is obtained by processing experimental data.
Fig. 7A shows data points of the cavity length of the fabry-perot interference cavity corresponding to the farthest end region of the H-shaped MEMS silicon diaphragm changing with time under the excitation of the acoustic wave with the frequency of 322Hz and the acoustic pressure of 270mpa, and a fitting curve thereof in the microphone under test according to embodiment 3 of the present invention. The difference of the cavity lengths corresponding to the adjacent wave crests and wave troughs is 282.4nm, so that the amplitude of the outermost area of the H-type MEMS silicon diaphragm is 141.2 nm. Fig. 7B shows data points and a fitted curve thereof of the amplitude of the farthest end region of the H-shaped MEMS silicon diaphragm under the excitation of the acoustic wave with the frequency of 622Hz and the acoustic pressure of 98mPa for the tested microphone according to the embodiment 3 of the present invention. It can be seen that the amplitude of the most distal region of the H-shaped diaphragm is 277 nm. Comparing the amplitudes measured under the two different frequency acoustic wave excitations, it can be known that the amplitude generated at the farthest end of the H-type MEMS silicon diaphragm when the H-type MEMS silicon diaphragm works in the bending mode is much larger than the amplitude generated in the swinging mode.
So far, the method for measuring the amplitude of the microphone diaphragm according to the third embodiment of the present invention has been described.
Although the embodiments of the present invention have been described in detail with reference to the accompanying drawings, it should be noted that the implementations not shown or described in the drawings or in the specification are all the forms known to those skilled in the art, and thus are not described in detail. Further, the above definitions of the various elements and methods are not limited to the various specific structures, shapes or arrangements of parts mentioned in the examples, which may be easily modified or substituted by those of ordinary skill in the art.
In summary, the invention provides a method and a device for measuring the amplitude of a microphone diaphragm, wherein an acoustic signal is modulated into an optical signal, a spectrum signal is demodulated by a fast demodulation device, and the amplitude of the microphone diaphragm is obtained by a peak-finding algorithm and fitting. The method can realize the vibration amplitude measurement of the vibration diaphragm of the microphone, is based on a conventional micro-displacement test system, has small volume, low cost and easy realization, is not only suitable for measuring the mechanical sensitivity of various existing microphones, but also can be used for measuring the vibration amplitude of the vibration diaphragm on line in the manufacturing process of the microphone, and creates favorable conditions for optimizing the manufacturing process, improving the consistency of devices and realizing the repeatable preparation of the microphone.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (11)
1. A microphone diaphragm amplitude measurement device, comprising: single mode fiber, surveyed microphone, sound source, light source, spectrum detection module and control and signal processing unit, wherein:
the single-mode optical fiber comprises a first end face and a second end face which are positioned at two ends, and the first end face is a plane vertical to the optical fiber axis;
the tested microphone is provided with a vibrating diaphragm with a reflective surface, and a local area of the vibrating diaphragm is right opposite to the first end face of the single-mode optical fiber to form a Fabry-Perot interference cavity;
the sound source is used for generating single-frequency sound waves to excite the diaphragm of the microphone to be tested to vibrate;
the light source is used for providing incident light which can be incident to the Fabry-Perot interference cavity through the single-mode optical fiber and generate interference light through the Fabry-Perot interference cavity;
the spectrum detection module is used for continuously detecting interference light generated by the Fabry-Perot interference cavity when a vibrating diaphragm of the microphone to be detected vibrates at a preset spectrum sampling rate to obtain a plurality of interference spectrums;
the control and signal processing unit is used for controlling the sound wave frequency and the sound pressure generated by the sound source and processing a plurality of interference spectrums output by the spectrum detection module so as to obtain a plurality of cavity lengths of the Fabry-Perot interference cavity during the vibration period of the vibrating diaphragm and determine the amplitude of a local area of the vibrating diaphragm according to the change of the cavity lengths along with time;
the determining the amplitude of the local area of the diaphragm according to the change of the plurality of cavity lengths with time specifically includes:
cavities corresponding by respective interference spectraThe long sums constitute an array (t)1、L1)、(t2、L2)…(tn、Ln) Substituting into the equation of vibration
Calculating the amplitude DeltaL of the local area of the tested microphone diaphragm, wherein n is the number of interference spectrums, and L0Is the cavity length, f, of the diaphragm in the rest state0Is the acoustic frequency, t is the time of day,
is the phase difference between the vibration of the diaphragm and the sound wave.
2. The microphone diaphragm amplitude measurement device of claim 1, wherein a distance between the first end surface of the single-mode optical fiber and a local region of the diaphragm facing the first end surface of the single-mode optical fiber is adjusted to cause the interference spectrum to have at least 1 peak and at least 1 valley; and/or
The preset spectrum sampling rate of the spectrum detection module is more than 2 times of the sound wave frequency generated by the sound source; and/or
Not less than 3 interference spectra are obtained by the spectrum detection module during each test.
3. The apparatus as claimed in claim 1, wherein the apparatus further comprises a precision moving platform for adjusting the position of the single-mode fiber with respect to the microphone, so that the first end surface of the single-mode fiber and the local region of the diaphragm of the microphone form the fabry-perot interference cavity.
4. The microphone diaphragm amplitude measurement device of claim 3, wherein the precision moving platform is provided with a microphone holder and a single-mode fiber holder, and the precision moving platform can translate, lift or rotate the microphone holder and/or the single-mode fiber holder.
5. The microphone diaphragm amplitude measurement device of claim 1, further comprising a fiber-optic circulator or a one-to-two fiber-optic splitter, the fiber-optic circulator or the one-to-two fiber-optic splitter comprising a first port, a second port, and a third port, wherein:
the first port is an input end and is connected with the light source through an optical fiber;
the second port is an output port and is connected with the spectrum detection module through an optical fiber;
and the third port is butted with the second end face of the single-mode optical fiber.
6. The microphone diaphragm amplitude measurement device of claim 1, characterized in that:
the microphone diaphragm amplitude measuring device also comprises a standard sound level meter or a standard microphone, and is used for measuring the sound pressure of sound waves generated by the sound source reaching the microphone diaphragm to be measured; and/or
The microphone diaphragm amplitude measuring device also comprises at least one single-tube video microscope which is used for monitoring the relative position between the first end surface of the single-mode optical fiber and the local area of the diaphragm of the microphone to be measured; and/or
The microphone diaphragm amplitude measuring device also comprises a case used for eliminating echoes, isolating noise and isolating vibration in the test process; and/or
The light source is an ASE light source or an LED light source or a halogen tungsten lamp, and the emission spectrum bandwidth of the light source is more than 20 nanometers; and/or
The spectrum detection range of the spectrum detection module covers the emission spectrum of the light source; and/or
The microphone to be detected is one of an electret microphone, an MEMS microphone, an optical fiber microphone and a grating microphone, or a component containing a diaphragm in the electret microphone, the MEMS microphone, the optical fiber microphone and the grating microphone; and/or
The vibrating diaphragm is a vibrating diaphragm formed by one vibrating diaphragm material of metal, glass, graphene, silicon, polymer, metal oxide and silicon nitride, or a composite vibrating diaphragm formed by a plurality of vibrating diaphragm materials.
7. A method of measuring an amplitude of a microphone diaphragm using the microphone diaphragm amplitude measuring apparatus according to any one of claims 1 to 6, comprising the steps of:
step A: the first end face of the single-mode optical fiber is right opposite to a local area of a diaphragm of a microphone to be detected so as to form a Fabry-Perot interference cavity;
and B: starting a light source and a spectrum detection module, and enabling incident light provided by the light source to be incident to the Fabry-Perot interference cavity through the single-mode optical fiber to generate interference light;
and C: controlling the sound source to emit at a frequency f0The spectrum detection module is utilized to continuously detect interference light generated by the Fabry-Perot interference cavity during the vibration period of the diaphragm of the microphone to be detected at a preset spectrum sampling rate, so as to obtain a plurality of interference spectrums;
step D: processing the plurality of interference spectrums output by the spectrum detection module by using a control and signal processing unit so as to obtain a plurality of cavity lengths of the Fabry-Perot interference cavity during the vibration period of the diaphragm, and determining the amplitude of a local area of the diaphragm according to the change of the cavity lengths along with time;
the determining the amplitude of the local area of the diaphragm according to the change of the plurality of cavity lengths with time specifically includes:
an array (t) is formed by the cavity lengths and the moments corresponding to the respective interference spectra1、L1)、(t2、L2)…(tn、Ln) Substituting into the equation of vibration
Calculating the amplitude DeltaL of the local area of the tested microphone diaphragm, wherein n is the number of interference spectrums, and L0Is the cavity length, f, of the diaphragm in the rest state0Is the acoustic frequency, t is the time of day,
is the phase difference between the vibration of the diaphragm and the sound wave.
8. The method according to claim 7, characterized in that step D comprises the following sub-steps:
substep D1: processing each interference spectrum by using smooth denoising and interpolation fitting algorithms respectively, and processing each interference spectrum at time t1～tnObtaining, wherein n is the number of interference spectra;
substep D2: respectively determining the wavelength lambda of two adjacent wave crests or two adjacent wave troughs in each interference spectrum after treatment1、λ2Based on the formula
Wherein L is the cavity length of the Fabry-Perot interference cavity, and the cavity length L corresponding to each interference spectrum is obtained by calculation1～Ln；
Substep D3: an array (t) is formed by the cavity lengths and the moments corresponding to the respective interference spectra1、L1)、(t2、L2)…(tn、Ln) Substituting into the equation of vibration
Calculating the amplitude DeltaL of the local area of the tested microphone diaphragm, wherein L0Is the cavity length, f, of the diaphragm in the rest state0Is the acoustic frequency, t is the time of day,
is the phase difference between the vibration of the diaphragm and the sound wave; or
The step D specifically comprises the following substeps:
sub-step D1': de-noising with smoothingAnd the interpolation fitting algorithm respectively processes each measured interference spectrum, and each interference spectrum is respectively processed at the moment t1～tnObtaining, wherein n is the number of interference spectra;
sub-step D2': respectively determining the wavelength lambda of a pair of adjacent peaks and troughs in each interference spectrum after processing1、λ2Based on the formula
Wherein L is the cavity length of the Fabry-Perot interference cavity, and the cavity length L corresponding to each interference spectrum is obtained by calculation1～Ln；
Sub-step D3': an array (t) is formed by the cavity lengths and the moments corresponding to the respective interference spectra1、L1)、(t2、L2)…(tn、Ln) Substituting into the equation of vibration
Calculating the amplitude DeltaL of the local area of the tested microphone diaphragm, wherein L0Is the cavity length, f, of the diaphragm in the rest state0Is the acoustic frequency, t is the time of day,
is the phase difference between the vibration of the diaphragm and the sound wave.
9. The method of claim 7, further comprising, after step B and before step C, the steps of:
step B': and enabling the first end face of the single-mode optical fiber to gradually approach to the local area of the vibrating diaphragm along the direction vertical to the first end face until the interference spectrum obtained by the spectrum detection module can generate at least 1 peak and at least one trough, and then stopping approaching.
10. The method of claim 9, wherein in step B', the position of the first end face of the single-mode optical fiber relative to the local region of the diaphragm is monitored using a monocular video microscope.
11. The method of claim 7, wherein the diaphragm of the microphone under test is exposed to air prior to testing.
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